The use of near infrared (NIR) radiation for diagnostic procedures in the human body has traditionally been limited by the inability to transmit NIR radiation into and through the body and extremities (see, for example, Handbook of Optical Biomedical Diagnostics, V Tuchin, Ed, SPIE Press, Bellingham Wash. (2002)). U.S. Pat. No. 6,230,046 to Crane et al showed that with sufficient amplification, transmitted NIR illumination may be used for both diagnostic and medical procedures involving vascular imaging. However, with this amplification, the imaging system must use a darkened environment and bandpass filters to limit interference from background light typically extant in medical settings.
The use of an NIR sensor and reflected or transilluminated NIR light to view both dermal and subdermal structures in the body is limited by the amount of light that is interacted with the body and is available for imaging on a detector, such as those commonly used in the art including charged coupled device (CCD) arrays, metal on silicon (MOS) arrays or image intensifier tubes (IIT) or combination of these. Image quality or resolution is directly related to the amount of light with image information that reaches the detector after interaction with the body minus the light that is captured that does not interact with the body. Light that does not contain image information is considered noise and degrades the image. For example, sunlight that is reflected from the surface of skin and entering the detector optics degrades the image in direct relationship to the amount of light intercepted by the detector.
Optical filtering to restrict the pass band of the detector to the light emitted by the illumination source according to Crane et al showed that NIR sensitive detectors could be used to image both dermal and subdermal structures such as veins and arteries. This works well for many illumination sources of visible lighting, but has limited applicability for sources that emit light in that portion of the NIR spectrum near or within the band used for image formation. Typical visible illumination sources such as fluorescent light bulbs have strong emission lines at wavelengths between 800 and 900 nm that represent noise in an NIR subdermal imaging system.